Aerial firefighting dump gate system

ABSTRACT

A gatebox system for delivering fire retardant fluid from a firefighting aircraft. A first and second gate opening are formed through a lower portion of a gatebox. The gates are hingedly connected along edges of the openings. One or two drive shafts in the gatebox are rotatable in gates-closing and gates-opening directions. Crank arms are fixed to the drive shafts and coupled to the gates by connecting links, which define an over-center geometry while the gates are at a closed position, such that weight of the fluid on the first gate induces torque on the drive shaft in the gates-closing direction. Rotation of the drive shafts in the gates-opening direction enables control of the fluid flow from the hopper according to an angular position of the drive shaft.

BACKGROUND OF THE INVENTION References to Related Applications

This is a continuation in part of application Ser. No. 16/030,147 filedon Jul. 9, 2018, now U.S. Pat. No. 11,046,433.

FIELD OF THE INVENTION

The present invention relates to firefighting aircraft fire retardantdump gates.

DESCRIPTION OF THE RELATED ART

Firefighting aircraft, also referred to as air tankers, carry a volumeof fire retardant, such as water or other chemicals, which are dumpedonto designated areas for fire control operations. The fire retardant iscarried in a tank or hopper within the aircraft and is released throughthe use of a dump gate. The release and targeting of the fire retardantis a critical operation due to the necessarily limited volume of fireretardant available on a given aircraft and the generally large areas offire being attacked. Targeting calculations involve the air speed,altitude, wind speed, rate of climb/descent, volume of fire retardant tobe dispersed, length and width of a predetermined target area, and therate at which the fire retardant is dumped from the dump gate. As such,control of the dump gate opening and rate of flow are critical fortargeting purposes.

U.S. Pat. No. 8,365,762, issued on Feb. 5, 2013 to Trotter, who is aninventor of the present disclosure, teaches a hydraulic control systemused to operate a dump gate in a firefighting aircraft. In that design,hydraulics are advantageously employed because of their reliability,their ability to apply substantial forces to a pair of gates, and theirability to firmly and quickly control the position of the dump gates. Afeedback control system was employed to provide precise position controlof the gates. This system has a record of proven performance in certainmodels of firefighting aircraft from Air Tractors, Inc. (Olny, Tex.),including the AT-802F “Fire Boss” aircraft.

While hydraulics have been successfully employed for dump gateoperation, hydraulics do carry certain liabilities. The hydraulic pump,actuators, reservoir, pipes and fittings are relatively heavycomponents, which weight must be deducted from the fire retardantpayload. Hydraulics also introduce a new dynamic system in an aircraft,which also carries existing dynamic systems, such as the aircraftelectric generators and storage batteries, and which might be more fullytaken advantage of Hydraulics also create maintenance issues andpotentials for leaking and other reliability issues. Thus, it can beappreciated that there is a need in the art for an improved dump gateand control system that addresses the problems in the prior art.

SUMMARY OF THE INVENTION

The need in the art is addressed by the systems as taught by the presentinvention. The present disclosure teaches a gatebox system for a hopperthat contains fluid in a firefighting aircraft. The gatebox systemincludes a box assembly with an upper portion adapted to receive thefluid from the hopper, and a first gate opening and a second gateopening formed through a lower portion of the gatebox. A first gate ishingedly connected along an edge of the first gate opening, and a secondgate is hingedly connected along an edge of the second gate opening. Adrive shaft is supported within the box assembly and is rotatable in agates-closing direction and a gates-opening direction. A first crank armis fixed to the drive shaft and coupled to the first gate by a firstconnecting link, which defines an over-center geometry while the firstgate is at a closed position, such that weight of the fluid on the firstgate induces torque on the drive shaft in the gates-closing direction.Similarly, a second crank arm is fixed to the drive shaft and coupled tothe second gate by a second connecting link, which define an over-centergeometry while the second gate is at a closed position such that weightof the fluid on the second gate induces torque on the drive shaft in thegates-closing direction. And wherein, rotation of the drive shaft in thegates-opening direction is coupled to the first and second gates by thefirst and second crank arms and the first and second connecting links toopen the first and second gates, to thereby enable control of the fluidflow from the hopper according to an angular position of the driveshaft.

In a specific embodiment of the foregoing gatebox system, the first andsecond connecting links engage the drive shaft while the first andsecond gates are at the closed positions to thereby preventover-rotation of the drive shaft in the gates-closing direction. Inanother specific embodiment, the first crank arm and the firstconnecting link further comprise plural crank arms and plural connectinglinks disposed between the drive shaft and the first gate, and thesecond crank arm and the second connecting link further comprise pluralcrank arms and plural connecting links disposed between the drive shaftand the second gate.

In a specific embodiment of the foregoing gatebox system, the first andsecond crank arms and the first and second connecting links areconfigured with a geometry whereby the first gate and the second gatesopen out of phase with one another as the drive shaft is rotated in thegate-opening direction.

In a specific embodiment, the foregoing gatebox system further includesan electric motor driving a gear reduction drive coupled to rotate thedrive shaft in both of the gates-opening and gates-closing directions.In a refinement to this embodiment, the gear reduction drive comprises aclutch operable to disconnect the drive shaft from the electric motor.

In a specific embodiment, the foregoing gatebox system further includesa servo-motor coupled to drive the drive shaft in either of thegates-opening or gates-closing directions. In a refinement to thisembodiment, the gatebox system further includes a control system coupledto the servo-motor to control the angular position of the drive shaft,and thereby control of the flow of fluid through the first and secondgates.

In a specific embodiment, the foregoing gatebox system further includesa position sensor coupled to the drive shaft that outputs a gateposition signal to the control system, and a current sensor couple tothe servo motor that outputs a motor current signal to the controlsystem, and wherein the control system defines a gates-closed positionof the first and second gates when the position signal indicates aclosed condition and the motor current signal exceeds a predeterminedcurrent threshold. In a further refinement to this embodiment, thecontrol system controls the flow of fluid from the first and secondgates by counting the number of revolutions of the servo-motor.

In a specific embodiment of the foregoing gatebox system, wherein thegatebox is installed in an aircraft having plural aircraft batteriesconnected in parallel, the gatebox system further includes a motor powersupply having a switching circuit connected to the plural aircraftbatteries, which operates to switch the plural aircraft batteries into aseries circuit to thereby increase the voltage available to drive theservo-motor.

In a specific embodiment of the foregoing gatebox system, wherein thegatebox is installed in an aircraft having an aircraft power supplyproviding a first voltage, the gatebox system further includes a motorpower supply coupled to the servo-motor, and a battery connected inseries with the aircraft power supply to thereby provide a drive voltageto the servo-motor that is greater than the first voltage.

In a specific embodiment, the foregoing gatebox system further includesan electric motor and a gear reduction drive coupled between the motorand the drive shaft to rotate the drive shaft in either of thegates-opening and gates-closing directions under motive force of themotor, and a clutch coupled to selectively disconnect the drive shaftfrom the electric motor, and a manual actuator coupled to the clutch toselectively disconnect the motor from the drive shaft, and therebyenable the first and second gates to open without use of the motor.

In a refinement to the foregoing embodiment, the gatebox system furtherincludes a clutch linkage disposed between the manual actuator and theclutch, and the clutch linkage is coupled to the drive shaft through ashaft crank arm, and actuation of the manual actuator applies rotationalforce to the drive shaft, through the shaft crank arm, in thegates-opening direction, to thereby rotate the drive shaft past theover-center condition to enable the first and second gates to fall openunder force of gravity.

In a further refinement to the foregoing embodiment, the clutch linkageis configured to disengage the clutch prior to applying rotational forceto the drive shaft. In another refinement, the gatebox system furtherincludes an interlock coupled between the clutch linkage and the motor,that operates to disable electric power to the motor upon actuation ofthe manual actuator.

The present disclosure teaches a gatebox system for a hopper thatcontains fluid in a firefighting aircraft, which includes a box assemblythat receives the fluid from the hopper, and has first and second gateopenings formed through a lower portion thereof, and first and secondgates hingedly connected along edges of the gates. First and seconddrive shafts are rotatably supported within the box assembly, and, firstand second cranks arm are fixed to the first and second drive shafts,respectively, and are coupled to the first and second gates by first andsecond connecting links. A shaft synchronizer engages the first andsecond drive shafts to synchronize their rotation in respectivegate-opening and gate-closing directions, and the shaft synchronizer hasan input coupler. An electric motor is coupled to urge rotation of theinput, and rotation of the input coupler induces synchronized rotation,through the shaft synchronizer, of both of the first and second driveshafts in the respective gates-opening and gates-closing directions,which are thereby coupled to the first and second gates by the first andsecond crank arms and the first and second connecting links to open andclose the first and second gates, and to thereby enable control of thefluid flow from the hopper according to angular positions of the inputcoupler.

In a specific embodiment of the foregoing gatebox system, the firstfirst and second crank arms and the first a second connecting links arearranged to define an over-center geometry while the first and secondgates are at closed positions, such that weight of the fluid on thefirst and second gates induces torque on the first and second driveshafts in the respective gates-closing directions.

In a specific embodiment of the foregoing gatebox system, the inputcoupler includes a portion of the first drive shaft, and the motor iscoupled to the portion of the first drive shaft.

In a specific embodiment of the foregoing gatebox system, the shaftsynchronizer includes first and second gears meshingly engaged with oneanother, and each is coupled to the first or second drive shafts,respectively.

In a specific embodiment of the foregoing gatebox system, the shaftsynchronizer comprises drive components selected from; a pair of meshedgears, a pair of sheaves coupled with a timing belt, a pair of sprocketscoupled by a roller chain, a pair of gears coupled by a geared rack, anda pair of crank arms coupled by a connecting link.

In a specific embodiment of the foregoing gatebox system, the first andsecond connecting links engage the first and second drive shafts whilethe first and second gates are at the closed positions to therebyprevent over-rotation of the first and second drive shafts in therespective gates-closing directions.

In a specific embodiment of the foregoing gatebox system, the firstcrank arm and the first connecting link further comprise plural crankarms and plural connecting links disposed between the first drive shaftand the first gate, and the second crank arm and the second connectinglink further comprise plural crank arms and plural connecting linksdisposed between the second drive shaft and the second gate.

In a specific embodiment of the foregoing gatebox system, the first andsecond crank arms and the first and second connecting links areconfigured with a geometry such that the first gate and the second gateopen out of phase with one another as the first and second drive shaftsare rotated in the gate-opening direction.

In a specific embodiment, the foregoing gatebox system further includesa transmission coupled between the electric motor and the input coupler,to thereby increase the available torque to drive the first and seconddrive shafts in both of the respective gates-opening and gates-closingdirections.

In a specific embodiment of the foregoing gatebox system, thetransmission includes a clutch operable to disconnect the input couplertherefrom.

In a specific embodiment, the the foregoing gatebox system furtherincludes a servo-motor connected to a servo-motor controller, andcoupled to the input coupler to thereby drive the first and second driveshafts in either of the respective gates-opening or gates-closingdirections. In a refinement to this embodiment, the servo-motor iselectrically arranged to function as a generator when driven by forcedapplied to the gates, to thereby deliver regenerative electrical powerback into said servo-motor controller. In anther refinement to thisembodiment, a manual OPEN and CLOSE actuator is coupled to theservo-motor controller, to enable manually selectable operation of thegates between open and closed positions. In another refinement to thisembodiment, the gatebox system further includes a control system coupledto the servo-motor to control the angular positions of the first andsecond drive shafts, and thereby control of the flow of fluid throughthe first and second gates. In a further refinement, the gatebox systemincludes a position sensor coupled to the input coupler that outputs agate position signal to the control system, and a current sensor coupledto the servo motor that outputs a motor current signal to the controlsystem, and wherein the control system defines a gates-closed positionof the first and second gates when the position signal indicates aclosed condition and the motor current signal exceeds a predeterminedcurrent threshold. In yet another refinement, the control systemcontrols the flow of fluid from the first and second gates by countingthe number of revolutions of the servo-motor.

In a specific embodiment, the foregoing gatebox system further includesa transmission coupled between the electric motor and the input couplerto thereby rotate the first and second drive shafts in either of therespective gates-opening and gates-closing directions under motive forceof the motors and, a clutch coupled to selectively disconnect thetransmission from the input coupler, and a manual actuator coupled tothe clutch to selectively disconnect the transmission from the inputcoupler, and thereby enable the first and second gates to open withoutuse of the motor. In a refinement to this embodiment, the gatebox systemfurther includes a clutch linkage disposed between the manual actuatorand the clutch, and, the clutch linkage is coupled to the input couplerthrough a shaft crank arm, such that actuation of the manual actuatorapplies rotational force to the input coupler, through the shaft crankarm, in the gates-opening directions, to thereby rotate the first andsecond drive shafts past their the respective over-center conditions toenable the first and second gates to fall open under force of gravity.In another refinement, the clutch linkage is configured to disengage theclutch prior to applying rotational force to the input coupler. In yetanother refinement, t3h gatebox further includes an interlock coupledbetween the clutch linkage and the motor, and operable to disableelectric power to the motor upon actuation of the manual actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a fire retardant delivery systemaccording to an illustrative embodiment of the present invention.

FIG. 2 is a drawing of a pilot interface according to an illustrativeembodiment of the present invention.

FIG. 3 is a perspective view drawing of a fire retardant gateboxaccording to an illustrative embodiment of the present invention.

FIG. 4 is a section view drawing of a fire retardant gatebox accordingto an illustrative embodiment of the present invention.

FIG. 5 is a section view drawing of a fire retardant dump gates anddrive linkages according to an illustrative embodiment of the presentinvention.

FIG. 6 is a section view drawing of a fire retardant dump gates anddrive linkages according to an illustrative embodiment of the presentinvention.

FIG. 7 is a section view drawing of a fire retardant dump gates anddrive linkages according to an illustrative embodiment of the presentinvention.

FIG. 8 is a diagram of a power supply according to an illustrativeembodiment of the present invention.

FIG. 9 is a diagram of a power supply according to an illustrativeembodiment of the present invention.

FIG. 10 is a perspective view drawing of an emergency dump linkageaccording to an illustrative embodiment of the present invention.

FIG. 11 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 12 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 13 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 14 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 15 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 16 is a diagram of an emergency drop linkage according to anillustrative embodiment of the present invention.

FIG. 17 is a section view drawing of a gear reduction transmission withclutch according to an illustrative embodiment of the present invention.

FIG. 18 is a section view drawing of a gear reduction transmission withclutch according to an illustrative embodiment of the present invention.

FIG. 19 is a section view drawing of a dual shaft gatebox assembly withthe gates closed according to an illustrative embodiment of the presentinvention.

FIG. 20 is a section view drawing of a dual shaft gatebox assembly withthe gates open according to an illustrative embodiment of the presentinvention.

FIG. 21 is a section view drawing of a dual shaft gatebox assembly withthe gates closed according to an illustrative embodiment of the presentinvention.

FIG. 22 is a section view drawing of a dual shaft gatebox assembly withthe gates open according to an illustrative embodiment of the presentinvention.

FIG. 23 is a top view drawing of a dual shaft gatebox assembly accordingto an illustrative embodiment of the present invention.

FIG. 24 is a top view drawing of a dual shaft gatebox assembly accordingto an illustrative embodiment of the present invention.

FIG. 25 is an end view drawing of a gear-coupled shaft synchronizeraccording to an illustrative embodiment of the present invention.

FIG. 26 is an end view drawing of a belt or chain coupled shaftsynchronizer according to an illustrative embodiment of the presentinvention.

FIG. 27 is an end view drawing of a pinion-gear and geared-rack typeshaft synchronizer according to an illustrative embodiment of thepresent invention.

FIG. 28 is an end view drawing of a gear-coupled shaft synchronizeremploying and idler gear according to an illustrative embodiment of thepresent invention.

FIG. 29 is an end view drawing of a pinion-gear and geared-rack typeshaft synchronizer according to an illustrative embodiment of thepresent invention.

FIG. 30 is an end view drawing of a crank arm type shaft synchronizeraccording to an illustrative embodiment of the present invention.

DESCRIPTION OF THE INVENTION

Illustrative embodiments and exemplary applications will now bedescribed with reference to the accompanying drawings to disclose theadvantageous teachings of the present invention.

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications, and embodimentswithin the scope hereof and additional fields in which the presentinvention would be of significant utility.

In considering the detailed embodiments of the present invention, itwill be observed that the present invention resides primarily incombinations of steps to accomplish various methods or components toform various compositions, apparatus and systems. Accordingly, theapparatus and system components and method steps have been representedwhere appropriate by conventional symbols in the drawings, showing onlythose specific details that are pertinent to understanding the presentinvention so as not to obscure the disclosure with details that will bereadily apparent to those of ordinary skill in the art having thebenefit of the disclosures contained herein.

In this disclosure, relational terms such as first and second, top andbottom, upper and lower, and the like may be used solely to distinguishone entity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. An element proceeded by “comprises a” does not,without more constraints, preclude the existence of additional identicalelements in the process, method, article, or apparatus that comprisesthe element.

In an illustrative embodiment of the present disclosure, the Air Tractor802F fire fighting aircraft is the host for the gatebox assemblytogether with its related control equipment. This is also referred to asa “firegate.” Functionally speaking, the gatebox is the discharge valvesystem used to dispense fire retardant from the aircraft, and plays acritical role in the efficient utilization of the limited quantity offire retardant available in any given drop flight. The Air Tractor 802Fis a single engine air tanker with an 800 gallon payload that is purposebuilt for aerial firefighting. The aircraft drops the payload through anopening in the belly of the fuselage. This disclosure contemplatesimprovement to the prior art gatebox systems, which is commerciallyreferred to as the third generation fire retardant drop system, (“GENIII FRDS”). The present disclosure presents an electrically drivenmechanical gate system, together with an electrical system, whichcontrols the position of the gate doors to meter the flow of fireretardant from the AT-802F fire retardant hoppers. Long term retardantand other liquid payloads may be used in the hoppers as necessary forvarious firefighting missions.

A typical fire retardant release takes a minimum of approximatelyone-half second, and up to a maximum of about 10 seconds depending ongate controller settings, which dynamically control the firegate openingsize and duration. The controller has an interface module located in thecockpit while all other electronic equipment is mounted outside of thecockpit. Reference is directed to FIG. 1 , for an introduction of thesystem components. The gatebox 64 and control system components includemultiple electrical boxes to perform various functions and a mechanicalgate system with moving doors coupled to an actuator. All components areprotected by circuit breakers of appropriate size. The primarycomponents include a pilot interface 52, a gate controller 50, a motorcontroller 56, an electric motor 58, a gatebox 64, a transmission 62,and an emergency dump system 68, 70. In addition, there is a powersupply 74 that interfaces with the aircraft power system 72.

The pilot interface 52 is powered by the gate controller 50 and is themeans by which various system settings are primarily controlled. Nowreferring to FIG. 2 , the pilot interface 52 consists of a displaymodule 51 and various switches and indicators. The display module 51 isin an aluminum case with a silicone membrane type keypad. The LCDdisplay 51 is mounted behind a sealed piece of glass. The pilotinterface 52 provides messages and system status to the pilot, andaccepts inputs from plural actuators 53, 55, 57, 73, 75, 77, 79, 81, 83,85, and 87 and one push button/rotary encoder. Plural indicating lampsare also provided; 59, 61, 63, 65, 67, 69, and 71.

The pilot interface 52 push buttons include a Mark button 53, which isused for telemetry system only, and defines points of interest. ADistress button 55 is also used for the telemetry system only, andactivates transmission of a distress signal. A Menu button 57 enters andexits controller menus operations. A Home button 77 returns the display51 to a home screen. A MSG (Message) button 73 is also used for thetelemetry system only, and receives text messages sent to the unit. ASelect actuator 75 is a scroll and select device used to access menuoptions present on the display 51.

The pilot interface 52 also comprises indicator lamps, including a timemode status lamp 59, which is related to GPS tracking intervals. It alsoincludes an ARMED status indicator 61, which will be more fullydiscussed hereinafter. It also includes an emergency dump (E-DUMP)system status indicator lamp 69, which will also be more fully discussedhereinafter. It also includes a satellite modem (SAT) connectivitystatus indicator 71, which is related to telemetry functions. It alsoincludes a GPS connectivity indicator 65, which is also related to gateand telemetry functions. It also includes a distance mode (DIST) statusindicator 63, which is related to GPS tracking intervals.

The pilot interface 52 also includes plural toggle switches below thedisplay area, as follows. An ARMED switch 79, which is turned on to armthe system prior to dumping fire retardant through the gatebox. There isalso a Gallons To Dump switch 81, which enables the pilot to adjust thevolume of fire retardant to be dumped. There is also a Coverage Levelswitch 83, which enables the pilot to set the fire retardant cover levelof each dump. There is a also a Gate Open/Close switch 85, which enablesthe pilot to drive the gates open or closed, and is also used tocalibrate the closed position setting. Finally, there is a FOAM switch87, which allows for injecting foam into the system.

Now referring back to FIG. 1 , the gate controller 50 is the maincontrol box for the system, and provides the following function. Thegate controller 50 accepts inputs from the pilot interface 52, therebyenabling the pilot to set system parameters. The gate controller 50connects to the various feedback devices such as sensors and switches.The gate controller 50 provides the microprocessors used to controllogic functions for the system. The gate controller 50 performscalculations for the requisite gate angle to meet targeted drop ratesbased on sensor inputs. The gate controller 50 provides feedback to themotor controller 56. The gate controller 50 performs passive diagnosticsand system self-tests. The gate controller 50 provides power and signalsto the pilot interface 52. The gate controller 50 contains anaccelerometer to sense the acceleration of the aircraft. The gatecontroller 50 provides Automated Flight Following (AFF) and AdditionalTelemetry Unit (ATU) functions. The gate controller 50 records andtransmits firefighting event data via cellular or satellite modems. Thegate controller 50 contains a GPS module to determine location ofaircraft.

Continuing in FIG. 1 , the motor controller 56 processes commands fromthe gate controller 50 and communicates them to the electric motor 58.The motor controller 56 also converts the 24 volt (nominal) aircraft buspower to three-phase AC power required to drive the electric motor,which is a three-phase rotating-field motor with a permanent magnetrotor. In other embodiments, a 48 volt (nominal) power supply isemployed to yield higher motor torque and power ratings. The motorcontroller may also maintain a motor shaft position and rotation countby reading an optional resolver 60 that rotates together with the motor58. Other sensor technologies could be employed for the resolverfunction including incremental encoders, absolute encoders, rotary andlinear potentiometers, linear LVDT or potentiometers with a crack arm,as are known to those skilled in the art. In the illustrativeembodiment, the motor is a Heinzmann GmbH (www.heinzmann.com) model PMS100 series permanent magnet synchronous motor.

Note that the gate controller 50 further includes an internal supervisorcircuit to provides redundancy by providing a discrete input signal tothe motor controller 56 to open the gates if a normal drop command doesnot initiate gate movement within 0.8 seconds. This supervisor circuitis hardware driven and requires no software within the gate controller50 to command the motor controller 56. It should be noted that as thegate box 64 opens the gates (not shown) the weight of the fire retardanttherein urges the gates to open with a substantial amount of force. Thisforce is coupled through the transmission 62 and into the motor 62,urging it to rotate more quickly. As such, the motor must act as a brakeagainst an overly-rapid and uncontrolled gate opening. Or, some sort ofmechanical brake may be required. In an illustrative embodiment, themotor 58 and motor controller 56 provide a regenerative braking actionwhereby that force is converted to electric current in the motor 56,which is back fed into the power supply 74, comprising the batteries(not shown). As such, regenerative braking is realized and the batteriesare somewhat recharged during the fire retardant dump process. Thisoffsets the electric power demand placed on the aircraft by the systemof the present disclosure.

The gatebox system, as generally depicted in FIG. 1 , includes a numberof system sensors that provide parametric inputs to the gate controller50. A hopper volume sensor (not shown) outputs a voltage proportional tothe rotary position of a hopper float shaft. The gate controller 50calculates the gallons in the hopper based on this voltage for useduring drops and for display to the pilot and ground loading crew. Thissensor is mounted onto the rear hopper of the aircraft. A gatebox anglesensor 66 outputs an analog voltage that is proportional to the rotaryposition of the gate drive shaft (discussed hereinafter). The gatecontroller 50 uses this signal when controlling the gatebox gate anglein normal mode only. In an alternative embodiment, a linear sensor (notshown) may be employed, which measures the gate opening directly, andwhich is also couple to the Gate Controller 50. When either of the anglesensor 66 or the linear sensor are employed, the use of the resolver 60is options. This is because where the gate position is measure, it isnot essential to keep track of the motor's annular position for thedetection of gate positions. These two approaches represent two optionsavailable to the designer.

An accelerometer (not shown) is provided within the gate controller 50,and provides the control system with a voltage proportional to theacceleration of the aircraft. This is used by the controller for flowrate and door angle calculations in normal mode only. In addition, aHall effect sensor (not shown) is internal to the motor and outputs asignal to the motor controller 56 for position feedback control. Atemperature sensor (not shown) also provides the motor controller 56with the internal temperature of the motor, which can be used fordiagnostics. Both sensor signals exit the motor 58 through a commoncable for connection to the motor controller 56.

Continuing in FIG. 1 , the electric motor 58 is an AC poweredservo-motor, which is used to open and close the gatebox gates. Thismotor 58 is controlled by the gate controller 50 through the motorcontroller 56 during normal system operation to precisely control theangle of the gatebox 64 gates (not shown) to achieve constant flow outof the aircraft hoppers (not shown). The motor 58 is coupled to a driveshaft (not shown) in the gatebox 64 by a splined connection to atransmission 62, which comprises a gear reduction therein. Thetransmission 62 reduces the motor 58 shaft speed to achieve anappropriate output speed. The transmission 62 also multiples the motor's58 output torque in order to provide sufficient torque to open and closethe gates (not shown). Note that the motor controller 56 converts DCinput power to a variable frequency and current three-phase AC power tothe motor to achieve control.

The primary source of power in FIG. 1 is the aircraft power bus 72,which typically provides 24 volts DC nominal power to the gatecontroller 50. In some embodiments, the motor controller 56 may beselected to operate on 24 volts. However, in other embodiments, themotor controller 56 is selected to operate on 48 volts DC (nominal). Thehigher voltage enables the use of motors with higher power and torqueratings. In order to provide a motor controller input voltage greaterthan the aircraft power bus 72 voltage, and power supply 74 is added,which provides the increased voltage. Details and options for achievingthis increased voltage will be more fully discussed hereinafter.

In the event of a complete failure of the gatebox system of FIG. 1 , itis necessary to provide an emergency dump system for safety reasons.This is achieved with an emergency dump actuator 68 that is coupled tothe electrical system through a switch 78, and to the transmission 62and gatebox 64 using a mechanical linkage 70. The transmission 62includes a clutch (not shown) that disengages the motor 58 from thegatebox 64 upon actuation of the emergency dump 68. Actuation alsoapplies a rotating force on the drive shaft (not shown) in the gatebox64 to move it past an over-center position, which enables the gates (notshown) to fall open and dump the fire retardant. The over-centermechanical arrangement will be more fully discussed hereinafter. Theswitch 78 disconnects the DC power supply 74 from the motor controller56 upon actuation of the emergency dump 68 to ensure that the motor 58cannot apply any rotational force to the system. This system and itsfunctions will be more fully discussed hereinafter.

The gatebox system (or “system”) can be operated in normal mode usingthe control logic to open and close the gates in response to a selectedCoverage Level and Gallons to Dump. In an alternative mode of operation,the system may be operated in a manual mode, where the gate controller50 functions are entirely omitted. In this mode, only OPEN and CLOSEactuators are provided, which directly control the motor controller 56.Such an arrangement is considerably less expensive to implement. In themanual mode, the operator uses a third party display and the OPEN andCLOSE switches to meter flow manually. Now, returning to the GateController 50 operated system, once the pilot initiates a drop bydepressing the drop trigger, the controller will open the doors andadjust the door angle to maintain a constant flow rate from the hoppers.When the selected gallons to dump have been evacuated, the doors closeto capture any remaining fluid in the hoppers. The control system willcompensate for various dynamics during the drop event. Table 1 presentsa summary of function of the system.

TABLE 1 Parameter Device Type Action Comments Dump Switch - Opens thegates when Located on Trigger INO, 1NC pressed, closes gates flightstick when released ARMED Switch, 2 pos, Arms FRDS system to StatusIndicator toggle locking detent enable high voltage to on Pilot motor,illuminate the Interface ARMED indicator light OPEN/ Switch, 3 pos,Opens or closes door System must be CLOSE momentary, when toggled ARMEDtoggle center rest Coverage Switch, 3 pos, Increases or decreases Setsthe desired Level +/− momentary, coverage level when flow rate fromtoggle center rest toggled the gate Gallons to Switch, 3 pos, Increasesor decreases Sets the desired Dump +/− momentary, the gallons to dumpvolume to drop center rest when toggled Foam Switch, 3 pos, Sets foaminjection Controls foam Set/Inject momentary, value or initiates foamsystem center rest injection Datawheel Push button, Rotation scrollsthrough Located on the rotary encoder menu selections, push PilotInterface selects current item Mark Switch, Creates points of Fortelemetry momentary interest system only Distress Switch, Transmits adistress For telemetry momentary message system only Menu Switch,Enters/exits controller momentary menus Home Switch, Returns display tomomentary Home screen MSG Switch, Receives text messages For telemetrymomentary sent to the unit system only

During normal operation of the system, the following operatingparameters exist:

-   -   A. Circuit breakers for the system are engaged to distribute bus        power from the aircraft to the gate control system    -   B. The system microprocessors boot up and current system        parameters are displayed on the Pilot Interface    -   C. Coverage Level and Gallons to Dump are adjusted to the        desired value by the pilot    -   D. The pilot toggles the ARMED switch to arm the system    -   E. The system is now in standby mode    -   F. The pilot depresses the drop trigger on the flight stick to        initiate a drop        -   a. The system opens the doors to maintain the desired flow            rate, once the desired volume has been released the doors            close automatically    -   G. Once the drop is complete, the pilot releases the drop        trigger. The pilot may choose to release the trigger to close        the doors prior to the release of the pre-selected volume        -   a. When the doors are open in any mode, if the pilot            released the drop trigger the doors will close    -   H. The system returns to standby mode and is ready for another        delivery cycle

Reference is directed to FIG. 3 , which is a perspective view drawing ofa fire retardant gatebox 2 according to an illustrative embodiment ofthe present invention. The gatebox 2 is a riveted aluminum structure 4that is mounted to the belly of the aircraft. The structure is primarilyassembled from 6061-T6 aluminum sheet. The gatebox 2 attaches to theairframe (not shown) using a flange and bolt pattern 6 on the upperportion thereof. Front and rear fiberglass fairings (not shown) areattach between the gatebox 2 and belly of the airframe (not shown) toprovide an aerodynamic profile. The Air Tractor AT-802F aircraftcomprises forward and rear fiberglass hoppers (not shown) that havethroats that exit at the belly of the aircraft to feed fire retardantinto the gatebox 2.

The gatebox 2 includes a first and second gate opening 7, 9 that eachhas a corresponding gate 8, 10 that is hinged along one edge of the gateopenings. A piano style hinge is appropriate, and an O-ring seal may bedisposed between the gate openings and the gates to provide a watertight seal when the gates 8, 10 are in a closed position to engage thegate openings 7, 9.

A drive shaft 12 is rotatably supported within the gatebox 2 and alignedalong the longitudinal axis of the aircraft in this embodiment. Thedrive shaft 12 is rotatable in both a gates-opening direction and agates-closing direction, which will be more fully discussed hereinafter.Plural sets of crank arms and connecting links 14 are disposed along thelength of the drive shaft 12 for opening and closing the gates 8, 10 byrotation of the drive shaft 12. Each set comprises a crank 22, 24, whichare fixed along the length of the drive shaft 12, and a correspondingconnecting link 26, 28 that are disposed between a distal end of thecrank arms 22, 24 and corresponding gate 8, 10. In this embodiment,three crank arms and connecting links are provided for each gate. Aminimum of one crank arm and connecting link is required for each gate.Thusly, rotation of the drive shaft 12 is converted to linear travel bythe crank arm and connecting link arrangement to push the gates open inthe gates-opening direction of rotation and pull the gates closed in thegates-closing direction.

Reference is directed to FIG. 4 , which is a section view drawing of afire retardant gatebox 2 according to an illustrative embodiment of thepresent invention. FIG. 4 corresponds with FIG. 3 . In FIG. 4 , theupper mounting flange 6 is defined by the gatebox 2 aluminum sheet 4structure, with the first gate opening 7 and the second gate opening 9formed through a lower portion thereof. A first gate 8 is hingedlyconnected along an edge of the first gate opening 7. The drive shaft 12has a first crank arm 22 fixed thereto, which is in-turn coupled fromits distal end to the first gate 8 by a first connecting link 26, asillustrated. Similarly, the second gate 10 is hingedly connected alongan edge of the second gate opening 9, and the drive shaft 12 also has asecond crank arm 24 fixed thereto, which is in-turn coupled from itsdistal end to the second gate 10 by a second connecting link 28, asillustrated. As noted above, in the illustrative embodiment, there arethree sets of crank arms and connecting links for each gate. Thusly, itcan be appreciated that rotation of the drive shaft 12 willsimultaneously open and close both gates 8, 10, depending on whether itis rotated in the gates-opening or gates-closing directions.

Reference is directed to FIG. 5 , which is a section view drawing of afire retardant gatebox with drop gates and drive linkages according toan illustrative embodiment of the present invention. FIG. 5 correspondswith FIG. 4 . In FIG. 5 , the gates 8, 10 are shown in their fullyclosed position. The gate openings 7, 9 are separated by a portion ofthe gatebox structure 30, which is used to form a water tight seal whilethe gates 8, 10 are closed. O-rings or other elastomeric seals areappropriate for this application. Such seals can be applied to the gateopenings 7, 9 or the gates 8, 10, or both. The drive shaft 12 can beseen above the gates 8, 10. The first gate 8 is connected to the driveshaft 12 by a first crank arm 22 and a first connecting link 26. Notethat the connecting link 26 is has an arcuate shape to facilitateclearance for the drive shaft 12. The second gate 10 is connected to thedrive shaft 12 by a second crank arm 24 and a second connecting link 28.Note that the connecting link 28 is has an arcuate shape to facilitateclearance for the drive shaft 12. Also note that the close clearancebetween the second connecting link 298 and the drive shaft 12 is suchthat rotation of the drive shaft 12 in the counter-clockwise directionwould result in engagement between the connecting link 28 and the driveshaft, which would prevent over-rotation of the drive shaft in thegates-closing direction. This is by design.

Now consider the geometry of the connecting links and crank arms in FIG.5 , which are shown in the closed position with an over-centerconfiguration. The second crank arm 24 has a pivot 34 at its distal end,which connects to the second connecting link 28, which in-turn connectsto a pivot 36 attached to the second gate. The centerline 38 between thecrank arm pivot 34 and the gate pivot 38 lies below the centerline ofthe drive shaft 12. As such, a downward load of fire retardant on thesecond gate will induce a rotation on the drive shaft 12 in thegates-closing direction (counter-clockwise in this view). Thusly, thedrive shaft needn't hold the gate closed because the second connectinglink 28 will engage the drive shaft 12 to prevent over-rotation in thegates closing direction. Other structure and stops could also beprovided to prevent such over rotation. This is an important feature ofthe present embodiment because it provides that the motor andtransmission do not have to be energized or locked to hold the gatescloses. It is a passive mechanical arrangement that holds the gatesclosed. Of course, the first crank arm 22 and first connecting link 26may provide the same over-center geometry.

Reference is directed to FIG. 6 , which is a section view drawing of afire retardant gatebox and drive linkages according to an illustrativeembodiment of the present invention. FIG. 6 corresponds with FIG. 5 .FIG. 6 illustrates two features of the present design. First, the changein linkage geometry away from the over-center condition, and second theimplementation of out of phase gate linkages. In this Figure, the driveshaft 12 has been rotated 42 in the gates-opening direction. As thishappens, the centerline 38 between the crank arm pivot 34 and gate pivot36 has moved above the centerline 32 of the drive shaft 12, and awayfrom the over-center condition. Therefore, the weight of the fireretardant on the gates 8, 10 will induce rotation of the drive shaft inthe gates-opening direction. This is important with respect to theemergency dump feature (described elsewhere herein) because it enablesmanual opening of the gates with minimal force and distance of movement.All that need occur is to disconnected the motor drive and transmissionfrom the drive shaft 12, and then apply just enough rotation in thegates-opening direction to move past the over-center condition. As soonas that occurs, the weight of the fire retardant will cause the gates tofall open and immediately drop the entire load of fore retardant.

The other feature illustrated in FIG. 6 is the out of phase linkarrangement. The rotational forces applied to the drive shaft 12 areprovided by the motor and transmission (not shown) and vary along thedistance of rotational travel of the drive shaft 12. The highest forcesoccur as the linkages pass through the over-center position, and as theseals around the gate openings are engaged. Since there are two gates,the forces occur in two parts, and the total force is approximatelytwice that of a single gate operating force. By adjusting the positionof the crank arms 24, 22, and/or the lengths of the crank arms andconnecting links 26, 28, the designer can adjust these force peaks to beout of phase with one another, and therefore spread them out over thedistance of rotational travel of the drive shaft 12. This has the effectof reducing the peak torque required from the motor and transmission. InFIG. 6 , it can bee seen that the second gate 10 has opening slightlymore than the first gate 8, and this illustrates the out of phaselinkage arrangement.

Reference is directed to FIG. 7 , which is a section view drawing of afire retardant dump gates and drive linkages according to anillustrative embodiment of the present invention. FIG. 7 correspondswith FIGS. 5 and 6 . In FIG. 7 , the weight of the fire retardant (notshown) has pushed the gates 8, 10 fully open and the fire retardant hasbeen completely dropped by the gates. The falling action of the gates 8,10 has been coupled through the connecting links 26, 28 and the crankarms 22, 24 and caused the drive shaft 12 to rotate fully 44 in thegates-open direction. The ability of the gates to fall open depends upondisconnection of the drive shaft 12 from the motor and transmission (notshown). If such a disconnect is not implemented, then the movement ofthe gates 8, 10 remains under control of the system, by the motor andtransmission.

Reference is directed to FIG. 8 , which is a schematic diagram of apower supply according to an illustrative embodiment of the presentinvention. As was discussed hereinbefore, modern aircraft commonlyprovide a DC power bus that provides 24-volt (nominal) power foraccessories. The present disclosure contemplates the use of 24-voltmotors and circuitry that can be directly coupled to such a power bus.However, the use of a higher voltage power supply offers certainadvantages, particularly with respect to the available power and torquein an electric motor of a given frame size. Higher voltage also enabledesigners to user lighter gauge wiring for a given motor rating, sincethe current is halved by a doubling of the voltage. FIG. 8 illustratesone technique for doubling the power supply voltage by rearranging theinterconnection amongst plural batteries provided with the aircraft.

FIG. 8 illustrates an aircraft that originally provides three 24-voltbatteries 80, 82, 84, which are originally connected in parallel todrive the aircraft power bus, at terminals 88. Under the teachings ofthe present disclosure, one of the batteries 84 is selected to berewired, and interconnected with a suitable DPDT relay 86. In itsunpowered state, the relay 86 couples the selected battery 84 inparallel with the non-selected batteries 80, 82. As such, the systemoperates as originally provided by the aircraft manufacture, in that allthree batteries are in parallel and are coupled to provide 24-volts tothe aircraft bus terminals 88. The aforementioned gate controller (notshown) is coupled to drive the relay 86 into a powered state when thesystems requires 48-volts for operation. This would occur at any timethe gate controller operates the drive motor. When this occurs, therelay 86 contacts switch states and the selected battery 84 istemporarily wired in series with the two unselected batteries 80, 82,and the 48-volts that that arrangement provides is delivered to themotor power terminal 90. When the motor operations are complete, therelay 86 is deenergized to return to the 24-volt operating mode.

Reference is directed to FIG. 9 , which is a diagram of a power supplyaccording to an illustrative embodiment of the present invention. FIG. 9illustrates an alternative circuit design for providing 48-volts to themotor and motor controller (not shown) of the present disclosure'sgatebox system. In this embodiment, an additional battery 94 is added tothe existing aircraft power system batteries 92. Note that only a singleaircraft battery 92 is illustrated in the circuit to simplify theschematic diagram. In actuality, there would be plural batteries at theconnection of battery 92. The aircraft batteries 92 deliver 24-volts tothe aircraft power bus at terminal 98. The additional battery 94 iswired in series with the aircraft power bus to provide 48-volts to themotor power supply terminals 48. In order to maintain a charge on theadditional battery a battery charger 96 is provided, which draws powerfrom the aircraft bus and charges the additional battery 94.

During normal operation, the gatebox system of the present disclosure isoperated by the gate controller utilizing an electric motor to operatethe gatebox gates, and the system is designed to be reliable and troublefree. However, as in all things aviation related, redundancy and manualalternatives are needed to be certain the pilot can safely return theaircraft to ground, or avoid a dangerous aeronautical situation. To thatend, the present disclosure provides an emergency drop system, which isalso referred to as an emergency dump or “E-Dump” system. This systemmust be operable without external power of any kind, and must beoperable by the pilot from the cockpit. Accordingly, the presentdisclosure teaches an independent, fully mechanical system configured sothat the gates can be opened in the event the gatebox system isinoperative. When power is off to the gatebox system, a mechanicalover-center latch arrangement is used to keep the gatebox gates closed.This latch system allows for a fire retardant load to be retained in thehoppers indefinitely without any action from the gatebox system, as wasdescribed above.

In order to open the gates using the emergency drop system, the pilotpushes an emergency drop handle forward in the cockpit causing a seriesof linkages to open the gatebox gates past the over-center latchedposition. The emergency drop system will function even if electricalpower to the system is lost. A series of limit switches are wired intothe system to cut control power to the gatebox system in the case whereelectrical power still exists. In one embodiment, the emergency drophandle is connected to a series of bell cranks and linkages as well astwo series connected electronic limit switches. When the lever is pushedforward, the limit switches are opened. This provides a signal to thegate controller that an emergency drop has been initiated. The gatecontroller then inhibits any commands to the electric motor. The leveralso enacts a mechanical series of linkages, which pull a release forkinside the transmission that is mounted to the front of the gatebox soas to decouple the electric motor's output shaft from the gate driveshaft. This action removes the motor from the mechanical system. Anotherpart of the emergency drop system linkage pulls a crank arm located onthe back side of the gatebox. This rotates the gatebox's drive shaft sothat the gate linkages are pulled back over-center. Once pulled into theun-latched position, the gates rotate to the fully open position due tothe weight of the fire retardant in the aircraft's hoppers, whichinstantly empties the aircraft fire retardant hoppers.

Reference is directed to FIG. 10 , which is a perspective view drawingof an emergency drop system linkage according to an illustrativeembodiment of the present invention. The end wall 200 of the gateboxserves as the mounting location for the mechanical components of theemergency dump system. External connections to this system include thepilot pull rod 218, which is connected to an operating handle in thecockpit, and, the clutch rod 224, which connects to a clutch located inthe transmission (not shown) at the opposite end of the gatebox. Theclutch rod 224 is illustrated in broken line because it is locatedbehind the gatebox. The drive shaft 202 extends through the end wall200, and is connected to a crank arm 204 supported within a drive shaftmount 206. Not that the drive shaft position sensor 208 is located onthe mount 206, and communicates the drive shaft position to the gatecontroller (not shown). A crank rod 210 is linked between the crank arm204 and a first end of a bell crank 214, which is rotatably supported ina suitable mount 212. A dump link 216 is connected to the opposite endof the bell crank 214, and is connected to the clutch rod 224 at itsopposite end. The connection between the dump link 216 and the clutchrod 224 is guided and limited in range of movement by a slot 222 in theclutch rod bracket 220. The pilot pull rod 218 is connected to the dumplink 216 along its length.

Reference is directed to FIGS. 11, 12, and 13 , which are operatingdiagrams of the emergency dump linkage system of FIG. 10 , and accordingto an illustrative embodiment of the present invention. The emergencydump system functions through three states, corresponding to FIGS. 11,12, and 13 , respectively. FIG. 11 shows the system in the normal statewhere the gates (not shown) are closed, the clutch (not shown) isengaged, and the drive shaft 202 has been rotated in the gates-closingdirection such that the aforementioned over-center condition holds thegates closed. Note that in these figures, the orientation of the driveshaft 202 and crank arm 204 have been rotated ninety degrees withrespect to the end wall 200 of the gatebox for visual clarity. FIG. 12shows the emergency dump linkage in the clutch-released state, and FIG.13 shows the linkage in the gates-open state.

In FIG. 11 , the crank arm 204 is located to the right, which is theover-center position, whereby the gates (not shown) hold themselvesclosed. The bell crank 214 is also rotated to the rights, as shown, byvirtue of the crank rod 210 linkage. The clutch rod 224 is forward,which is the clutch-engaged position. The pilot pull rod 218 is also inthe forward position. Note that “forward” means to toward the front ofthe aircraft, which is up in these drawing figures. In FIG. 12 , thepilot has pulled 226 the pilot pull rod 218 partially rearward toactivate the second state of the linkage system. The pilot pull rod 218pulls 226 the dump link 216 rearward, which pulls 228 the clutch rod 224rearward, thereby disengaging the clutch (not shown). The movement 228of the clutch rod 224 is limited by the slot 222 in the clutch rodbracket 220. Once this limit of movement is reached, the dump link 216begins rotating the bell crank 214 to the left, transitioning to theopen state of FIG. 13 .

In FIG. 13 , the pilot pull rod 218 has pulled 230 fully rearward, whichrotates 232 the bell crank 214 to the left. This action causes the crankrod 210 to pull 234 the crank arm 204, thereby rotating 236 it to theleft, and past the aforementioned over-center condition. The weight ofthe fire retardant (not shown) on the gates (not shown) promptly forcesthe gates open, and dumping the fire retardant from the hoppers.

Reference is directed to FIGS. 14, 15, and 16 , which are emergency dumplinkage diagrams according to an illustrative embodiment of the presentinvention. This emergency dump system functions through three states,corresponding to FIGS. 14, 15 , and 16, respectively. FIG. 14 shows thesystem in the normal state where the gates (not shown) are closed, theclutch (not shown) is engaged, and the drive shaft 302 has been rotatedin the gates-closing direction such that the aforementioned over-centercondition holds the gates closed. FIG. 15 shows the emergency dumplinkage in the clutch-released state, and FIG. 16 shows the linkage inthe gates-open state.

The linkage arrangement in FIGS. 14, 15, and 16 are attached to the rearbulkhead 300 of the gatebox. The drive shaft 302 is supported on a driveshaft mount 304, and has a crank arm 306 attached to its end, whichenables rotation of the drive shaft 302 by the various linkages. Thisembodiment comprises two levers that enable operation, and these includethe crank lever 317 and the clutch lever 312. The clutch lever 312pivots about a clutch lever pivot 322 on a clutch lever mount 310. Thecrank lever 317 pivots about a crank lever pivot 318 that is connectedto the clutch lever 312, as illustrated. A crank rod 308 is connected toa distal end of the crank arm 306 and to a crank rod pivot 320 locatedon the clutch lever 312, as illustrated. Note that the crank rod pivot320 and the clutch lever pivot 322 are aligned, one above the other, butnot connected, in the aforementioned first and second states. A pilotpull rod is connected to a distal end of the crank lever 317. A clutchrod is connected 330 to a distal end of the clutch lever 312, and itsmovement is limited by a slot 326 in a clutch rod mount 324, asillustrated.

In FIG. 14 , the pilot pull rod 316 is in the forward position (towardthe front of the aircraft, and up in the drawing figure). The clutch rod328 is also in the forward position, where the clutch (not shown) isengaged. The crank arm 306 is to the right, and the drive shaft 302 isin the over-center position, holding the gates (not shown) closed asdiscussed hereinbefore. In FIG. 15 , the pilot has pulled 332 the pilotpull rod 316 rearward. This action rotates 334 the crank lever 317 andthe clutch lever 312 downward (counter-clockwise in the figures).Rotation of the clutch lever 312 pulls 336 the clutch rod 328 rearward,disengaging the clutch (not shown). The extent of this movement 336 islimited by the clutch slot 326 in the clutch rod mount 324. Once thelimit of the clutch slot is reached, then further rearward movement 338(FIG. 16 ) of the pilot pull rod 317 results in rotation 340 of thecrank lever 317.

In FIG. 16 , the pilot pull rod 316 has been pulled 338 to its rearwardextent, and the crank lever 317 has been rotated 340 to its full extent.This action causes the crank lever 317 to rotate about the crank leverpivot 318, and pull the crank rod 308, to thereby rotate the drive shaft302 past the over-center condition. This action causes the gates (notshown) to drop open, as discussed hereinbefore. It is noteworthy toconsider the utility of having the clutch lever pivot 322 and the crankarm connection point 320 aligned with one another while the crank arm308 is full to the right. With this, pulling (322 in FIG. 15 ) the pilotpull rod 316 and rotating 334 the crank lever produces no force on thecrank rod 308. This allows the full effort of the pilot's action tofirst disengage the clutch by rotating the clutch lever 312 first, andnot beginning rotation of the crank lever 317 until the clutch rod 328has engaged the rearward end of the slot 326. After that occurs, thenall of the pilot's pull force is directed to pulling the crank arm 306and drive shaft 302 back over-center.

Reference is directed to FIGS. 17 and 18 , which are a section viewdrawings of a gear reduction transmission with clutch according to anillustrative embodiment of the present invention. This devicecorresponds to item 16 in FIG. 3 . FIG. 17 illustrated the transmissionwith the clutch 166, 162 engaged, and FIG. 17 with the clutch 166, 162disengaged. The transmission comprises a housing 150, which encloses andsupports a range of shafts, gears and bearings. The servo-motor 152 ismounted to the exterior of the housing 150, and presents a drive gear154 within the housing 150. A first gear reduction is achieved bymeshing the drive gear 154 with a first driven gear 156. This force isapplied through shaft 157 to the next gear reduction set of gears 158and 160. This force is coupled, in turn, to shaft 164. Shaft 164 issplined to a clutch cog 166, which is shiftable to either engage theinterior of clutch gear 162, or allows clutch gear 162 to free wheel. Ineither case, clutch gear 162 meshes with output gear 172, which is fixedto the output shaft 174. The output shaft 174 is attached to theaforementioned drive shaft (not shown) in the gatebox (not shown). Inother illustrative embodiments, the clutch arrangement 162, 164, 166 isimplemented in alternative configurations. For example, the clutchfunction can be implemented using an off-the-shelf gear box as thetransmission, and then employ a similar fork arrangement to engage anddisengage a mating set of splines, or hardened pin and dogs that engageone anther. The functional aspect of this and other arrangements is tomechanically disengage the gearbox and motor from the drive shaft 174,including coupling the clutch operation to the aforementioned emergencyrelease system, as will be appreciated by those skilled in the art.

Operation of the clutch is accomplished by sliding the clutch cog 166along its splined connection to shaft 164 to either engage or disengageclutch gear 162. This is accomplished by moving shift fork 168 byapplying a pulling force 180 at the distal end of shift rod 176. This isaccomplished by the aforementioned clutch rod in the emergency dumpsystem. A spring 170 is provided within the transmission housing 150 toreturn the clutch 162, 166 to the engaged condition. A weather seal boot178 is provided about the shift rod 176.

Referring back to FIGS. 3, 4, 5, 6, and 7 , it is noted that a singledrive shaft 12 employed pairs of crank arms 22, 24 and connecting links26, 28 to drive the pair of gates 8, 10, in the opening and closingdirections. That drive shaft 12 was driven through a transmission 16 byan electric motor 18. In an alternative embodiment now presented, a pairof drive shafts may be employed. The two shafts are mechanically coupledtogether using a shaft synchronizer, which may employ one of servaldesigns, as will be more fully discussed hereinafter. The two shafts maybe driven in a common direction of rotation (“common rotation”) or maybe driven in opposite directions of rotating (“counter-rotation”), withcranks arms and connecting links that are arranged to manage andsynchronize gate movement in both the gates-opening and gates-closingdirections. Note that “synchronization” does not necessarily mean thegates move in identical or identically symmetrical fashion. Rather, themovement of the gates is synchronized to be repeatable, and may employnon-symmetrical movement to facilitate fire retardant flow rates,driving force requirements, emergency release operation, as well asother considerations.

Reference is directed to FIG. 19 , which is a section view drawing of adual shaft gatebox 202 assembly with the gates 216, 218 in the closedposition, and according to an illustrative embodiment of the presentinvention. The gate box 202 has an attachment flange 200 for mating withthe aircraft fluid hopper (not shown) at its upper portion. A pair ofgates 216, 218 are hinged 220, 222 along corresponding openings 226, 228in the gate box 202, as illustrated. The openings 226, 228 are separatedby a center portion 224, which serves as a seal point around a portionof the perimeter of openings 226, 228. There are two drive shafts 204,206 arranged in parallel in the gate box 202, and generally disposedabove their respective gates 216, 218. The two drive shafts 226, 228have corresponding sets of crank arms 208, 210 connected tocorresponding connecting links 212, 214, which are arranged so thatrotation of the drive shafts 204, 206 urges the gates 216, 218 inrespective gates-opening and gates-closing directions.

Reference is directed to FIG. 20 , which is a section view drawing of adual shaft gatebox assembly 202 with the gates 216, 218 open accordingto an illustrative embodiment of the present invention. FIG. 20corresponds with FIG. 19 , but in FIG. 20 , the drives shafts 204, 206have been rotated 230, 232 in the gates-opening direction so as to openthe gates 216, 218. As such, the gates 216, 218 have moved away from thecenter portion 224, and any fire retardant (not shown) in the systemwill have been dispensed. Note that the drive shafts 204, 206 arerotated 230, 232 in counter-rotation directions. The crank arms 208, 210have moved in a downward direction, causing the crank arms 212, 214 todrive the gates 216, 218 open. Reversing the rotation would close thegates. Note that with the counter rotation of shafts 204, 206, thecomponents can be symmetrical about a vertical centerline, whichsomewhat simplifies the design arrangement and mechanical calculations,as will be appreciated by those skilled in the art.

It should be noted that the specific geometry of the drive shafts 204,206, the crank arms 208, 210, and the first and second connecting links212, 214 provides a wide range of opportunities to the system designer.The individual drive shafts may synchronized to operate in the same oropposing directions of rotation, and may be positioned and spaced apartto satisfy system requirements and physical limitations. The crank armscan be positioned at any angle with respect to the drive shaftorientation, and may extend to any suitable distance from the driveshaft centerlines. The connecting links may be routed between the twodrives shafts, as illustrated in FIGS. 19 and 20 , or may be routedabout the outboard sides of the drive shafts. Furthermore, the amount ofangular rotation required to move the gates from fully closed to fullyopen is also a design option available according to this range ofgeometries. This enables management of the motor drive system power andtorque requirement and how they are utilized, as will be appreciated bythose skilled in the art. In other embodiments, the connecting links212, 214 employ a flexible member, such as chain, cable or links (notshown). Since the bulk of the flow control occurs in the gates-openingdirection, a taught flexible member will provide the requisite openingcontrol. The aforementioned over-center geometery is still achieved byselecting the orientation of the crank arms 208, 210 such that theflexible connecting links wrap somewhat about the drive shafts 204, 206at the gates closed position.

Reference is directed to FIG. 21 , which is a section view drawing of adual shaft gatebox assembly 202 with the gates 216, 218 closed accordingto an illustrative embodiment of the present invention. This embodimentpresents the same gate box assembly 202 as in the prior figures, butwith common rotation of the two drive shafts 204, 206. It will be shownhereinafter, that common versus counter rotation designs affect theoptions for design of the shaft synchronizer (not shown in this FIG. 21). The first drive shaft 204 employs the same crank arm 208 position andthe same connecting link 212 arrangement as the immediately previoustwo-shaft embodiment. However, the second drive shaft 206 employs acrank arm 211 that is positioned differently, and a different connectinglink 215 coupled to the second gate 218 such that clockwise rotation, asviewed in the drawing figure, of the second drive shaft drives theseance gate 218 in the gates-opening direction. An over-center geometryis still employed for both connecting links 212, 215, as discussedhereinbefore.

Reference is directed to FIG. 22 , which is a section view drawing of adual shaft gatebox assembly 202 with the gates 216, 218 open accordingto an illustrative embodiment of the present invention. FIG. 22corresponds with FIG. 21 . In FIG. 21 it is shown that the first andsecond drive shafts 202, 206 have been rotated 234, 236 in the clockwisedirections (as illustrated) such that the respective crank arms 208, 211and connecting links 212, 215 have driven the gates 216, 218 fullytoward the gates open direction. Reversing rotation of the shafts 204,206 would drive the gates in the gates-closing direction.

Reference is directed to FIG. 23 , which is a top view drawing of a dualshaft gatebox assembly 202 according to an illustrative embodiment ofthe present invention. The mounting flange 200 is presented with the twoopenings 226, 228 formed through the assembly 202, and which are closedby gates 216, 218 in this view. The first drive shaft 204 is rotatablesupported by end bearing/seals 221, 223. Likewise, the second driveshaft 206 is rotatable supported by end bearing/seals 225, 227. Thefirst drive shaft 204 has three cranks arms 208 fixed to rotatetherewith, and which are coupled to three connecting links 212, whichare in-turn coupled to the first gate 216. Likewise, the second driveshaft 206 has three cranks arms 210 fixed to rotate therewith, and whichare coupled to three connecting links 214, which are in-turn coupled tothe second gate 218. This is a counter-rotation embodiment. A shaftsynchronizer 238 is coupled to both the first drive shaft 204 and thesecond drive shaft 206, and functions to urge them in counter-rotationfashion. The first drive shaft 204 extends through the shaftsynchronizer and further coupled to the output of a transmission 240,which is, in turn, driven by an electric motor 242. The transmission 240also presents a clutch operating lever 241, as presented hereinbefore.Note that the shaft synchronizer 238 may be placed along the two driveshafts 204, 206 at any location. For example, it may be placed insidethe assembly, as illustrate by broken lines 244. The shaft synchronizermay also be placed at the opposite end of the assembly, as illustratedby broken lines 246

Reference is directed to FIG. 24 , which is a top view drawing of a dualshaft gatebox assembly 202 according to an illustrative embodiment ofthe present invention. FIG. 24 corresponds with FIG. 23 , however, inFIG. 24 , the shaft synchronizer 248 is located within the transmission240. As such, the transmission has two outputs that are coupled to thefirst drive shaft 204 and second drive shaft 206, respectively.

Reference is directed to FIG. 25 , which is an end view drawing of agear coupled shaft synchronizer 250 according to an illustrativeembodiment of the present invention. The first and second drive shafts204, 206 are presented with their respective crank arms 208, 210, forreference. A first spur gear 252 is fixed to the first drives shaft 204,and a second spur gear 254 is fixed to the second drive shaft 206. Thespur gears 252, 254 are arranged to mesh with one another and thuslyinduce counter-rotation 256, 258 of the drive shafts 204, 206 withrespect to one anther. Either shaft may be driven by the transmission,which will induce counter rotation in either case.

Reference is directed to FIG. 26 , which is an end view drawing of abelt or chain coupled shaft synchronizer 260 according to anillustrative embodiment of the present invention. The first and seconddrive shafts 204, 206 are presented with their respective crank arms208, 210, for reference. A first cogged belt sheave, or a firstsprocket, 262 is fixed to the first drive shaft 204. And, a secondcogged belt sheave, or a second sprocket, 264 is fixed to the seconddrive shaft 206. A timing belt, or a roller chain, 266 is routed aboutthe sheaves/sprockets to synchronize their rotation in a common-rotation268, 270 fashion. Either shaft may be driven by the transmission, whichwill induce common-rotation in either case.

Reference is directed to FIG. 27 , which is an end view drawing of apinion gear and geared-rack type shaft synchronizer 272 according to anillustrative embodiment of the present invention. The first and seconddrive shafts 204, 206 are presented with their respective crank arms208, 210, for reference. A first pinion gear 274 is fixed to the firstdrives shaft 204, and a second pinion gear 276 is fixed to the seconddrive shaft 206. The pinion gears 274, 276 are arranged to mesh with ageared-rack 278, which is slidable retained in place, to thusly inducecommon-rotation 275, 277 of the drive shafts 204, 206 with respect toone anther. Either shaft may be driven by the transmission, which willinduce common rotation in either case.

Reference is directed to FIG. 28 , which is an end view drawing of agear coupled shaft synchronizer 279 employing an idler gear 2897according to an illustrative embodiment of the present invention. Thefirst and second drive shafts 204, 206 are presented with theirrespective crank arms 208, 210, for reference. A first spur gear 281 isfixed to the first drives shaft 204, and a second spur gear 283 is fixedto the second drive shaft 206. The spur gears 281, 283 are arranged tomesh with and idler gear 287 disposed therebetween, and thusly inducecommon-rotation 289, 291 of the drive shafts 204, 206 with respect toone anther. Either shaft 204, 206, or the idler gear 287, may be drivenby the transmission, which will induce common-rotation in either case.

Reference is directed to FIG. 29 , which is an end view drawing ofanother pinion gear and geared-rack type shaft synchronizer 280according to an illustrative embodiment of the present invention. Thefirst and second drive shafts 204, 206 are presented with theirrespective crank arms 208, 210, for reference. A first pinion gear 282is fixed to the first drives shaft 204, and a second pinion gear 284 isfixed to the second drive shaft 206. The pinion gears 282, 284 arearranged to mesh with a dual sided geared-rack 285, which is slidableretained in place along a diagonal path between the pinion gears 282.284, to thusly induce counter-rotation 286, 288 of the drive shafts 204,206 with respect to one anther. Either shaft may be driven by thetransmission, which will induce common rotation in either case.

Reference is directed to FIG. 30 , which is an end view drawing of acrank arm type shaft synchronizer 290 according to an illustrativeembodiment of the present invention. The first and second drive shafts204, 206 are presented with their respective crank arms 208, 210, forreference. A first crank arm 292 is fixed to the first drives shaft 204,and a second crank arm 294 is fixed to the second drive shaft 206. Thecrank arms 292, 294 are coupled together by a connecting link 296, tothusly induce common-rotation 298, 300 of the drive shafts 204, 206 withrespect to one anther. Either shaft may be driven by the transmission,which will induce counter rotation in either case. With this embodiment,shaft rotation is limited to somewhat less than one hundred eightydegrees.

Thus, the present invention has been described herein with reference toa particular embodiment for a particular application. Those havingordinary skill in the art and access to the present teachings willrecognize additional modifications, applications and embodiments withinthe scope thereof.

It is therefore intended by the appended claims to cover any and allsuch applications, modifications and embodiments within the scope of thepresent invention.

What is claimed is:
 1. A gatebox system for a hopper that contains fluidin a firefighting aircraft, comprising: a box assembly that receives thefluid from the hopper, having first and second gate openings formedthrough a lower portion thereof; first and second gates hingedlyconnected along respective edges of said first and second gate openings;first and second drive shafts, rotatably supported within said boxassembly; first and second crank arms fixed to said first and seconddrive shafts, respectively, and coupled to said first and second gatesby first and second connecting links, respectively; a shaft synchronizerengaged with said first and second drive shafts to synchronize rotationthereof in respective gate-opening and gate-closing directions, andhaving an input coupler; an electric motor coupled to said input couplerto urge rotation thereof, and wherein rotation of said input couplerinduces synchronized rotation, through said shaft synchronizer, of bothof said first and second drive shafts in said respective gates-openingand gates-closing directions, and wherein said synchronized rotation isthereby coupled to said first and second gates by said first and secondcrank arms and said first and second connecting links to open and closesaid first and second gates, and to thereby enable control of the fluidflow from the hopper according to angular positions of said inputcoupler.
 2. The gatebox system of claim 1, and wherein: said first andsecond crank arms and said first and second connecting links arearranged to define an over-center geometry while said first and secondgates are at closed positions, such that weight of the fluid on saidfirst and second gates induces torque on said first and second driveshafts in said respective gates-closing directions.
 3. The apparatus ifclaim 1, and wherein: said input coupler includes a portion of saidfirst drive shaft, and wherein said motor is coupled to said portion ofsaid first drive shaft.
 4. The apparatus if claim 1, and wherein: saidshaft synchronizer includes first and second gears meshingly engagedwith one another, and each coupled to said first or second drive shafts,respectively.
 5. The apparatus if claim 1, and wherein: said shaftsynchronizer comprises drive components selected from; a pair of meshedgears, a pair of gears meshed with a common idler gear, a pair ofsheaves coupled with a timing belt, a pair of sprockets coupled by aroller chain, a pair of gears coupled by a geared rack, and a pair ofcrank arms coupled by a connecting link.
 6. The gatebox system of claim1, and wherein said first and second connecting links engage said firstand second drive shafts while said first and second gates are at saidclosed positions to thereby prevent over-rotation of said first andsecond drive shafts in said respective gates-closing directions.
 7. Thegatebox system of claim 1, and wherein: said first crank arm and saidfirst connecting link further comprise plural crank arms and pluralconnecting links disposed between said first drive shaft and said firstgate, and said second crank arm and said second connecting link furthercomprise plural crank arms and plural connecting links disposed betweensaid second drive shaft and said second gate.
 8. The gatebox system ofclaim 1, and wherein: said first and second crank arms and said firstand second connecting links are configured with a geometry such thatsaid first gate and said second gate open out of phase with one anotheras said first and second drive shafts are rotated in said gate-openingdirection.
 9. The gatebox system of claim 1, and further comprising: atransmission coupled between said electric motor and said input coupler,to thereby increase the available torque to drive said first and seconddrive shafts in both of said respective gates-opening and gates-closingdirections.
 10. The gatebox system of claim 9, and wherein: saidtransmission is coupled through a clutch operable to selectivelydisconnect said input coupler therefrom.
 11. The gatebox system of claim1, further comprising: a servo-motor controlled by a serve-motorcontroller, and coupled to said input coupler to thereby drive saidfirst and second drive shafts in either of said respective gates-openingor gates-closing directions.
 12. The gate box system of claim 11, andwherein: said servo-motor is electrically arranged to function as agenerator when driven by forced applied to said first and second gates,to thereby deliver regenerative electrical power back into saidservo-motor controller.
 13. The gatebox system of claim 11, furthercomprising: manual OPEN and CLOSE actuators coupled to said servo-motorcontroller, to thereby enable manually selectable operation of saidfirst and second gates between open and closed positions.
 14. Thegatebox system of claim 11, further comprising: a control system coupledto said servo-motor controller to control the angular positions of saidfirst and second drive shafts, and thereby control of the flow of fluidthrough said first and second gates.
 15. The gatebox system of claim 14,and further comprising; a position sensor coupled to said input couplerthat outputs a gate position signal to said control system; a currentsensor coupled to said servo motor that outputs a motor current signalto said control system, and wherein said control system defines agates-closed position of said first and second gates upon receipt ofsaid position signal that indicates a closed condition and upon receiptof said motor current signal that exceeds a predetermined currentthreshold.
 16. The gatebox system of claim 15, and wherein: said controlsystem controls the flow of fluid from said first and second gates bycounting the number of revolutions of said servo-motor.
 17. The gateboxsystem of claim 1, and further comprising: a transmission coupledbetween said electric motor and said input coupler to thereby rotatesaid first and second drive shafts in either of said respectivegates-opening and gates-closing directions under motive force of saidmotor; a clutch coupled to selectively disconnect said transmission fromsaid input coupler; a manual actuator coupled to said clutch toselectively disconnect said transmission from said input coupler, andthereby enable said first and second gates to open without use of saidmotor.
 18. The gatebox system of claim 17, further comprising: a clutchlinkage disposed between said manual actuator and said clutch, andwherein said clutch linkage is coupled to said input coupler through ashaft crank arm, and wherein actuation of said manual actuator appliesrotational force to said input coupler, through said shaft crank arm, insaid gates-opening directions, to thereby rotate said first and seconddrive shafts past their said respective over-center conditions to enablesaid first and second gates to fall open under force of gravity.
 19. Thegatebox system of claim 18, and wherein: said clutch linkage isconfigured to disengage said clutch prior to applying rotational forceto said input coupler.
 20. The gatebox system of claim 18, furthercomprising: an interlock coupled between said clutch linkage and saidmotor, and operable to disable electric power to said motor uponactuation of said manual actuator.